Why breathability is the difference between comfort and a soggy trudge

On a long climb in the fells, you generate a tremendous amount of heat. Your body responds by sweating, and that moisture has to go somewhere. If your waterproof jacket cannot let it escape, you will end up soaked from the inside out, even if the rain never touches your skin. That is the cruel irony of waterproof clothing: the very feature that keeps the weather out can trap your own steam in. In persistent drizzle and a strong headwind, the problem is compounded. You cannot simply take your jacket off, because the wind and rain will chill you quickly. So you need a waterproof that breathes efficiently, and you need to know how to help it do its job.

Ventilation is not a luxury — it is a tool

The most effective breathability feature on any waterproof is a pit zip. These are zips under the arms that allow you to dump heat and moisture directly from the hottest part of your torso. On a steep ascent, open them wide. You will feel the difference within minutes. Many jackets also have chest pockets that double as vents, and two-way front zips that let you open the jacket from the bottom while keeping the top closed against the rain. Use them. Adjustable cuffs and hem drawcords help you seal out wind when you stop, but on the move you want air circulating. The trick is to modulate: open up on the climb, close down on the descent or when the wind picks up. That constant adjustment is part of the skill of fell walking.

• Pit zips: the most effective way to dump heat on a climb. Open them early, before you start to overheat.
• Two-way front zip: open from the bottom to let air in while keeping the top sealed against rain.
• Chest pockets: many double as vents when left open, but check they have mesh backing.
• Adjustable cuffs and hem: seal out wind when you stop, but keep them loose on the move.

Understanding fabrics and construction

Breathability is measured in grams of moisture vapour per square metre per 24 hours (g/m²/24h) or as a RET value, where lower is better. Numbers help, but they do not tell the whole story. A three-layer construction, where the membrane is bonded to both an outer face fabric and an inner liner, generally offers the best balance of durability and breathability. Two-and-a-half-layer jackets are lighter and more packable, but they can feel clammy against the skin. Look for a durable water repellent (DWR) finish on the outer fabric. This makes rain bead up and roll off, preventing the face fabric from becoming saturated. If the outer fabric wets out, the membrane cannot breathe, no matter how advanced it is. So DWR is not just about staying dry on the outside; it is essential for breathability.

Fit and layering for active climbs

A waterproof that is too tight will restrict your movement and compress your layers, reducing the air gap that helps moisture escape. Too baggy, and it will flap in the wind, letting rain in at the cuffs and hem. You want enough room for a base layer and a light midlayer, but not so much that the jacket looks like a tent. Pay attention to the hood: it should adjust to fit over a helmet or a hat without obscuring your vision. If you carry a rucksack, the shoulder straps and back panel will block breathability. There is no way around this entirely, but you can choose a rucksack with a suspended mesh back panel to allow some airflow. Otherwise, accept that your back will be damp, and choose a base layer that wicks and dries quickly.

Care and maintenance: keep it breathing

Your waterproof will only perform if you look after it. Dirt and body oils clog the membrane and the DWR, so wash your jacket regularly. Use a pure soap or a specialist tech wash — never biological detergent or fabric softener, which leave residues that destroy breathability. Follow the manufacturer's instructions, but generally a warm wash and a low tumble dry will reactivate the DWR. If water stops beading on the surface, re-proof it with a spray-on or wash-in DWR treatment. Store your jacket loosely, not crammed into a stuff sack, and avoid leaving it in a hot car. A well-cared-for jacket can last for years and keep you comfortable on countless climbs.

• Wash with a pure soap or tech wash — never biological detergent or fabric softener.
• Tumble dry on low to reactivate the DWR; check the care label first.
• Re-proof with a spray-on or wash-in treatment when water stops beading.
• Store loosely, away from heat and sunlight.

When the weather wins: strategies for persistent drizzle

Sometimes, despite your best efforts, you will get wet. Persistent drizzle and strong wind are a classic combination in the British hills, and no fabric can cope perfectly. In those conditions, focus on managing your comfort rather than staying perfectly dry. Wear a synthetic base layer that moves moisture away from your skin, and consider a thin fleece or grid fleece midlayer for warmth. If you are wild swimming, you will be wet anyway, so a waterproof is more about protecting you from wind chill on the walk back. Take your time, adjust your ventilation often, and remember that being damp is not the same as being cold. Keep moving, eat something, and you will get through it. The hills will still be there tomorrow.